Ionic liquid temperature sensor

ABSTRACT

A temperature sensor having a capillary tube or stem, sealed at both ends, with a thin bore defined therein is applied to the measurement of temperatures having a range of about −100° to +400° Centigrade. A bulb comprising a liquid reservoir, is provided at one end of the capillary tube, in liquid communication with the bore, and is generally filled with an ionic thermometric liquid. In the operation of the temperature sensor, temperature is measured by the height of the liquid in the bore.

TECHNICAL FIELD

[0001] This invention relates to a temperature sensor, and moreparticularly to a temperature sensor comprising a holder and an ionicliquid contained therein.

BACKGROUND OF THE INVENTION

[0002] Various types of temperature sensors are known includingliquid-in-glass (LIG) thermometers, bimetallic thermometers, resistancethermometers, thermocouples, and radiometers. Depending upon thetemperature to be measured, the required accuracy of the measurement,and other factors such as durability or cost, one type of temperaturesensor may be preferable over another.

[0003] For instance, LIG thermometers are standard equipment atlaboratories and surface weather stations. LIG thermometers have a fineglass bore and a fluid reservoir. Operation depends on the thermalexpansion of the liquid contained in the glass envelope. The sensitivityof the LIG thermometer depends inversely on the diameter of the bore ofthe tube and on the relative expansion coefficients of the liquid andglass. The desired temperature range is the main criterion in the choiceof the thermometric liquid.

[0004] The most common liquids used in LIG thermometers are themolecular liquids mercury (Hg) and ethanol. Hg LIG thermometers areinexpensive, durable, accurate and easily calibrated. Another advantageof the Hg LIG thermometer is its high temperature range (the upperoperating temperature limit for a Hg LIG thermometer is about 350° C.).Several disadvantages are that Hg is not be useful in low temperaturesituations because Hg freezes at about −39° C., that Hg responds slowlyin response to changes in temperature, and that Hg is highly volatileand toxic at low concentrations. Hg also poses an environmental hazardassociated with the storage and disposal of broken Hg LIG thermometers.

[0005] For temperature measurements below −39° C., LIG thermometerscontaining ethanol are commonly used. The ethanol LIG thermometer has afreezing point of about −110° C. and a boiling point of about 78° C.Ethanol has a faster response time and is less hazardous than Hg.However, fluid loss by evaporation is hard to avoid with ethanol and theupper operating temperature of 78° C. limits the utility of ethanol LIGthermometers over a wide temperature range.

[0006] For many applications, the desirable temperature range is −70 to370° C. Therefore, two LIG thermometers must used in such a situation,an ethanol thermometer for low temperatures and a Hg thermometer forhigh temperatures.

[0007] In addition to the LIG thermometer, another commonly usedtemperature sensor is the bimetallic thermometer. Bimetallicthermometers are found in household central heating and air conditioningsystems. Bimetallic thermometers rely on the differential thermalexpansion of two metals bound together in a strip. They are cheap,durable, easily calibrated and can be used for thermographs. However,they require frequent calibration to maintain accuracy and they exhibitslow response times.

[0008] Yet another commonly used temperature sensor is the thermocouple.Thermocouples are used for in situ observations at locations wired to acomputer network. Electrical and electronic thermometric devices delivera rapid response, are durable and accurate over a broad temperaturerange. However, thermocouple and thermistor devices require expensiveancillary equipment and electronics to operate.

[0009] Still another device for temperature measurement is theradiometer. Radiometers are used for remote temperature observations.Radiometers permit measurement of temperature by detecting theabsorption of emitted radiation. They are expensive specialist devicesmost commonly used for remote sensing on meteorological satellites.

[0010] The present invention provides one solution to the limitations ofthe currently available temperature sensors as is discussed in thedisclosure that follows. Here, a temperature sensor comprised of aholder containing an ionic liquid delivers a wider working temperaturerange than most other temperature sensors, is economical, easy tocalibrate, and the ionic liquid has low toxicity.

BRIEF SUMMARY OF THE INVENTION

[0011] The present invention is directed to a temperature sensorcomprised of an ionic liquid or mixtures thereof contained inside aholder.

[0012] In one embodiment, the temperature sensor is a holder using athermometric liquid. The sensor comprises a thermometer having anelongated vessel and a reservoir for liquid. The thermometer, further,comprises a bore, within the elongated vessel, the bore being in liquidcommunication with the reservoir. In a preferred embodiment, a pluralityof graduations are associated with the elongated vessel, such that thegraduations can express a range of temperatures equivalent to about−100° to about +400° Centigrade. The liquid in the thermometer rises orfalls, within the bore, depending on the temperature ambient to thethermometer.

[0013] In a preferred embodiment of the present invention the liquid isa thermometric ionic liquid that includes either a contrast or coloringmedium or dye such that the level of the liquid in the bore can be moreeasily seen. As a result of the use of the ionic liquids of the presentinvention, the thermometer can measure temperatures in a range of about−100° to about +400° Centigrade.

[0014] In a temperature sensor of a preferred embodiment, the spacewithin the bore is a vacuum. Further, as a result of the liquid used,the volume of liquid in the bore is dependent on temperature.

[0015] Also, the temperature sensor of the preferred embodiment can becreated from a transparent material, such as glass or plastic.

[0016] The ionic liquid is made up of organic cations and eitherinorganic or organic anions or mixtures thereof.

[0017] A cation of an ionic liquid is preferably one whose structurecorresponds to a formula selected from the group consisting of

[0018] wherein R¹ and R² are independently hydrido, a C₁-C₆ alkyl groupor a C₁-C₆ alkoxyalkyl group, and R³, R⁴, R⁵, R⁶, R⁷, R⁸ and R⁹ (R³-R⁹),when present, are independently a hydrido, a C₁-C₆ alkyl, a C₁-C₆alkoxyalkyl group or a C₁-C₆ alkoxy group. It is to be noted that thereare two iosmeric 1,2,3-triazoles. It is preferred that all R groups notrequired for cation formation be hydrido.

[0019] A cation that contains a single five-membered aromatic ring thatis free of fusion to other ring structures is more preferred. Exemplarycations are illustrated below wherein R¹, R², and R³-R⁵, when present,are as defined before. A preferred organic cation is a1-C₁-C₆-alkyl-3-methylimidazolium or a C₁-C₆alkoxyalkyl-3-methylimidazolium cation.

[0020] The anions of the ionic liquid can be hydrophilic or hydrophobic.An illustrative anion is selected from the group consisting of ahalogen, pseudohalogen, a C₁-C₆ carboxylate, tetrafluoroborate,hexafluorophosphate, a polyfluoro C₂-C₆ carboxylate,bis(trifluoromethane-sulfonyl)imide, trifluoromethanesulfonate, and thelike.

[0021] A preferred ionic liquid is 1-butyl-3-methylimidazoliumbis(trifluoromethanesulfonyl)imide ([C₄mim] [Tf₂N]). Another preferredionic liquid is 1-ethyl-3-methylimidazolium tetrafluoroborate ([C₂mim][BF₄]).

[0022] In another embodiment, a first ionic liquid is combined with asecond ionic liquid in order to reduce viscosity and depress thesolidification point. The second ionic liquid can be a colored ionicsalt such as imidazolium tetrachlorometallate salts.

[0023] In yet another embodiment, a solvent (non-ionic liquid) can beadded to the ionic liquid.

BRIEF DESCRIPTION OF THE DRAWING

[0024]FIG. 1 is a perspective view of a temperature sensor of thepresent invention.

DETAILED DESCRIPTION OF AN ILLUSTRATIVE

[0025] Embodiment of the Present Invention

[0026] Although the present invention is susceptible of embodiment invarious forms, there is shown in the drawing a presently preferredembodiment that is discussed in greater detail hereafter. It should beunderstood that the present disclosure is to be considered as anexemplification of the present invention, and is not intended to limitthe invention to the specific embodiment illustrated. It should befurther understood that the title of this section of this application(“Detailed Description of an Illustrative Embodiment of the Device ofPresent Invention”) relates to a requirement of the United States PatentOffice, and should not be found to limit the subject matter disclosedherein.

[0027] Referring now to the drawing, a typical temperature sensor,commonly referred to as a thermometer 10 is shown. Thermometer 10 is ofthe “liquid-in-glass” type thermometer that commonly containthermometric, or temperature sensitive, liquid such as mercury oralcohol. It will be understood, by persons having skill in the art, thatwhile “glass” has been used in the description of the present invention,any thermal conductive materials, having typical thermometer properties(such as transparency, strength, scratch resistance, ability towithstand sterilization, etc.), such as certain plastics, may be usedwithout departing from the novel scope of the present invention.

[0028] Thermometer 10 comprises a capillary tube or stem 12, sealed atboth ends, having a, typically thin, bore 14 defined therein. A bulb 16,comprising a liquid reservoir, is provided at one end of capillary tube12, and is generally filled with a thermometric liquid 18. Bulb 16,which seals the first end of capillary tube or stem 12, is incommunication with bore 14, and bore 14 can be formed, integrally, withbulb 16. In the operation of a liquid-in-glass thermometer, temperatureis measured by the height of the liquid in bore 14. The liquid 18 iscaused to rise, or fall, as a result in the change in pressure, withinbore 14, caused by the increase or decrease in the temperature of thebody being measured.

[0029] Liquid 18 is preferably colored so that it can be easily seenwithin the capillary tube or stem 12 of the thermometer 10. It will beunderstood by persons having skill in the art that a naturally coloredthermometric liquid, or one that naturally provides a contrast with thematerials used to make-up the capillary tube or stem 12 of a thermometer10, can be used, without addition of color or contrast materials,without departing from the novel scope of the present invention.

[0030] In the present invention, an ionic liquid is the thermometricliquid 18 used in thermometer 10. A more detailed discussion of acontemplated ionic liquid useful in the present invention is providedbelow.

[0031] Thermometer 10 further comprises graduations 20, of the typetypically found on thermometers, to provide a means for determining thetemperature of the body being tested. It will be understood, by personshaving ordinary skill in the art, that the graduations provided can beof any temperature scale, including but not limited to Centigrade orFahrenheit, without departing from the novel scope of the presentinvention. Further, the graduations, which can be of any size, shape orcolor, can be applied to thermometer 10 (or any part thereof orassociated therewith) in any manner known in the art, including byetching the graduations onto the thermometer body, painting thegraduations thereon, using decals, associating the thermometer with abacking material having a scale thereon, or associating the thermometerwith projected or electronic graduations, all without departing from thenovel scope of the present invention.

[0032] In a preferred embodiment of the present invention, thegraduations include a range of graduations of between about −100° andabout +400° Centigrade. It also will be understood that thermometer 10,of the present invention, can be constructed without graduations,without departing from the novel scope of the present invention.

[0033] Ionic liquids are liquids comprised of discrete ions havingsubstantially no vapor pressure and an exceptionally wide temperaturerange that can be from about −90° C. to about 400° C. [Holbrey et al.,Clean Prod. Proc., 1999, 1, 233; Welton, Chem. Rev., 1999, 99, 2071;Keim et al., Angew. Chem. Int. Ed., 2000, 39, 3772].

[0034] Most ionic liquids are comprised of an organic cation and ananion that can be inorganic or organic, but is usually weaklycoordinating or contains a diffuse negative charge. The range ofavailable ionic liquids is vast and potentially unlimited. About 10¹⁸individual ionic liquids can be prepared by simple variations in thealkyl-chain substitution patterns of the cations currently utilized forthe preparation of ionic liquids [Holbrey et al., Clean Prod. Proc.,1999, 1, 233]. This number is likely to be significantly underestimatedif other substituents, for example alkyloxy chains, cation types, aniontypes, and mixtures of two or more cations, anions or both areconsidered.

[0035] The most common organic cations used in ionic liquids aresubstituted pyridinium, pyridazinium, pyrimidiinium, pyrazinium,pyrazolium, imidazolium, oxazolium, triazolium, thiazolium,pyrrolidinium, piperazinium, quinolinium, isoquinolinium, ammonium, andphosphonium derivatives. A cation of an ionic liquid preferablycorresponds in structure to a formula selected from the group consistingof

[0036] wherein R¹ and R² are independently hydrido, a C₁-C₆ alkyl groupor a C₁-C₆ alkoxyalkyl group, and R³, R⁴, R⁵, R⁶, R⁷, R⁸ and R⁹ (R³-R⁹),when present, are independently a hydrido, a C₁-C₆ alkyl, a C₁-C₆alkoxyalkyl group or a C₁-C₆ alkoxy group. More preferably, both R¹ andR² groups are C₁-C₄ alkyl, with one being methyl, and R³-R⁹, whenpresent, are preferably hydrido. It is preferred that all R groups notrequired for cation formation be hydrido.

[0037] Exemplary C₁-C₆ alkyl groups and C₁-C₄ alkyl groups includemethyl, ethyl, propyl, iso-propyl, butyl, sec-butyl, iso-butyl, pentyl,iso-pentyl, hexyl, 2-ethylbutyl, 2-methylpentyl and the like.Corresponding C₁-C₆ alkoxy groups contain the above C₁-C₆ alkyl groupbonded to an oxygen atom that is also bonded to the cation ring. Analkoxyalkyl group contains an ether group bonded to an alkyl group, andhere contains a total of up to six carbon atoms.

[0038] A cation that contains a single aromatic five-membered ring thatis free of fusion to other ring structures is more preferred. Exemplarycations are illustrated below wherein R¹, R², and R³-R⁵, when present,are as defined before.

[0039] Of the more preferred cations that contain a single five-memberedring free of fusion to other ring structures, an imidazolium cation thatcorresponds in structure to Formula A is particularly preferred, whereinR¹, R², and R³-R⁵, are as defined before.

[0040] A 1,3-di-(C₁-C₆-alkyl)-substituted-imidazolium or1,3-di-(C₁-C₆-alkoxyalkyl)-substituted-imidazolium ion is a moreparticularly preferred cation; i.e., an imidazolium cation wherein R³-R⁵of Formula A are each hydrido, and R¹ and R² are independently each aC₁-C₆-alkyl or a C₁-C₆-alkoxyalkyl group. More preferably still, one ofthe 1,3-di-C₁-C₆-alkyl groups is methyl.

[0041] A 1-(C₁-C₆-alkyl)-3-(methyl)-imidazolium [C_(n)-mim, where n=1-6]cation or a C₁-C₆ alkoxyalkyl-3-methylimidazolium cation is morepreferred, and a halogen is a preferred anion. Such a more preferredcation is illustrated by a compound that corresponds in structure toFormula B, below, wherein R¹ is a C₁-C₆-alkyl or a C₁-C₆-alkoxyalkylgroup.

[0042] Most preferably, both nitrogen substituents are C₁-C₆-alkylgroups and one of the 1,3-di-C₁-C₆-alkyl groups is methyl, the other ofthe R¹ and the R² C₁-C₆-alkyl groups is C₁-C₄-alkyl, and the R³-R⁵groups are hydrido.

[0043] The phrase “when present” is often used herein in regard tosubstituent R group because not all cations have all of the numberedgroups.

[0044] The phrases “substantial absence” and “substantially free” areused synonymously to mean that less than about 5 weight percent water ispresent, for example. More preferably, less than about one percent wateris present in the composition. The same meaning is intended regardingthe presence of a nitrogen-containing base.

[0045] The anions of the ionic liquid can be hydrophilic or hydrophobic.Exemplary hydrophilic anions include halogen, pseudohalogen, and C₁-C₆carboxylate. Exemplary hydrophobic anions include tetrafluoroborate (BF₄⁻), hexafluorophosphate (PF₆ ⁻), polyfluoro C₂-C₆ carboxylate such astrifluoroacetate (F₃CCO₂ ⁻), pentafluoropropionate (F₅C₃O₂ ⁻),bis(trifluoromethane-sulfonyl)imide (Tf₂N⁻), trifluoromethanesulfonate(Tf⁻), and the like. Hydrophobic anions that contain covalently bondedfluorine atoms are particularly preferred. Additional illustrativehydrophobic ionic liquids are disclosed in U.S. Pat. No. 5,827,602.

[0046] The anions commonly used include inorganic halogens andpseudohalogens (chloride, bromide, nitrate, sulfate, alkylsulfate,sulfonate), organic carboxylates (acetate, lactate), fluorinated(tetrafluoroborate, hexafluorophosphate, trifluorosulfonate,trifluoroacetate, bis(trifluoromethanesulfonyl)imide,bis(perfluoroethylsulfonyl)imide) and halometallate (for examplechloride-AlCl₃ compositions) anions.

[0047] It is preferred that all R groups that are not required forcation formation; i.e., those other than R¹ and R² for compounds otherthan the imidazolium, pyrazolium, triazolium, pyrrolidinium andpiperadinium cations shown above, be hydrido. Thus, the cations shownabove preferably have a structure that corresponds to a structure shownbelow, wherein R¹ and R² are as described before.

[0048] A comparison of the working temperature range among an ionicliquid and some typical thermometric liquids is shown in Table 1. Asshown in the table, the ionic liquid has a wide working temperaturerange. TABLE 1 Working Temperature Liquid Range, ° C. Mercury −35 to 350Ethanol −80 to 60  Pentane −200 to 30  Toluene −80 to 100 [C₂mim] [BF₄]  −80 to 400^(a)

[0049] Exemplary liquification temperatures [i.e., melting points (MP)and glass transition temperatures (Tg)] and decomposition temperaturesfor illustrative 1,3-di-C₁-C₆-alkyl imidazolium ion-containing [(mim)]ionic liquids wherein one of R¹ and R² is methyl are shown in Table 2below. Data for other representative ionic liquids containing1-alkyl-pyridinium cations are shown in Table 3 below. TABLE 2 Liquifi-cation Decomposition Temperature Temperature Ionic Liquid (° C.) (° C.)Citation* [C₂mim] Cl 64 285 a [C₃mim] Cl 282 a [C₄mim] Cl 41 254 b[C₆mim] Cl −69 253 g [C₈mim] Cl −73 243 g [C₂mim] I 303 a [C₄mim] I −72265 b [C₄mim] [PF₆] 10 349 b [C₂mim] [PF₆] 58-60 375 c, a [C₃mim] [PF₆]40 335 a [iC₃mim] [PF₆] 102 a [C₆mim] [PF₆] −61 417 d [C₄mim] [BF₄] −81403, 360 d, e [C₂mim] [BF₄] 6 412 a, e [C₂mim] [C₂H₃O₂] 45 c [C₂mim][C₂F₃O₂] 14 About 150 f

[0050] TABLE 3 Liquification Decomposition Temperature Temperature IonicLiquid (° C.) (° C.) [1-butyl-3- 37 347 methylpyridinium] [PF₆][1-butyl-4- 3 358 methylpyridinium] [PF₆] [1-hexyl-4- 39methylpyridinium] [PF₆] [4-phenylpropyl- 2 163-474 pyridinium] [PF₆][3-n-butyl - 0 125-444 pyridinium] [PF₆] [1-butyl-4- −24 332methylpyridinium] [BF₄] [1-butyl-4- 32 214 methylpyridinium] Cl[1-hexyl-4- 63 218 methylpyridinium] Cl

[0051] Not all combinations of cations and anions result in ionicliquids. Thus, in some examples, high melting solids can be produced,but those solids can be readily identified and not used. The systematicstudy of the molecular features of the cation and anion governing theformation of low melting ionic liquids is the subject of activeresearch, both to understand ionic liquid systems and to predict newexamples.

[0052] Ionic liquids that melt below room temperature are referred to asroom temperature ionic liquids. A contemplated ionic liquid is liquid ator below a temperature of about 200° C., preferably below a temperatureof about 150° C. and above a temperature of about −50° C. Examples ofsuch liquids include [C₂mim]Cl/AlCl₄, [C₂mim] [BF₄], [C₄mim] [PF₆], andemim[NTf₂], wherein “mim” is a 1-substituted-3-methylimidazolium ion and“e” or “C₂” is 1-ethyl and C₄ is 1-butyl. More preferably, acontemplated ionic liquid is liquid (molten) at or below a temperatureof about 120° C. and above a temperature of about −44° C. Mostpreferably, the ionic liquid is liquid (molten) at ambient temperature.The liquid range of these ionic liquids can be from about −72° C. toover 350° C.

[0053] In the pure form, many of the ionic liquids form viscous glasseson cooling below room temperature, which can limit the lower operationaltemperature of a LIG containing such ionic liquid. The solidificationpoint and viscosity of ionic liquids can be reduced by admixing with oneor more other ionic liquids or with another liquid material or organicsolvent, producing a formulation. Such admixture has been shown, inseveral studies, to significantly reduce the viscosity of the admixture.

[0054] In evaluating individual ionic liquids or mixtures that can beused as thermometric fluids, a range of features needs to be considered:the working temperature range, the linear expansion coefficient of theliquid over the operational temperature range, the stability of theionic liquid, and the environmental impact of spills or breakage.

[0055] Of the known ionic liquids with published rheological properties,those containing perfluorinated anions have the lowest viscosity, andthis is often coupled to low melting points. From this aspect,tetrafluoroborate or bistrifylimide ionic liquids appear to offer apreferred viscosity/temperature profile. However, in the pure form, thebistrifylimide salts have well defined crystallization points and freezeabove −25° C., which could limit low temperature applications.

[0056] A formulation in which two or more ionic liquids are mixed offersa preferred option for reducing the solidification temperatures of thesystems by suppressing the melting/freezing point and by decreasingviscosity. This has been demonstrated, for example by MacFarlane andco-workers [Sun et al., J. Phys. Chem. B, 1998, 102, 8858] forquaternary ammonium systems with mixed cations in which certaincompositions suppress the melting point of the mixture by up to 40° C.The second ionic liquid can itself be a colored ionic salt such as animidazolium tetrachlorometallate salt such as [C₄mim]₂[PdCl₄] (brown) or[C₄mim]₂[NiCl₄] (blue), or the colorant can be dissolved or dispersed inthe ionic liquid.

[0057] The ionic liquid is contained within any convenient holder.Preferably the holder is partially translucent or transparent. Theholder can be composed of glass or more preferably a flexible plastic,although other materials such as metals or ceramics can also be used.

[0058] Although there are few data available on the toxicological andenvironmental effects of ionic liquids, it is believed that the effectof ionic liquids in the environment should be the sum of the two (ormore) component ions. The activity of some imidazolium salts has beenreported as antielectrostatic and antifungal. The acute toxicity of1-hexyloxymethyl-3-methylimidazolium tetrafluoroborate [Pernak et al.,Ind. Eng. Chem. Res., 2001] has been investigated and the LD₅₀ for ratswas reported as 1400 mg/kg. Cations containing short chain alkylsubstituents rather than ether groups are thought to have even lowertoxicity.

[0059] It should also be noted that many existing ionic liquids arestructurally related or comparable to known quaternary salts, forexample alkylammonium, alkylpyridinium, and alkylphosphonium salts, thatare widely used in industry and also in domestic environments in soaps,detergents, personal products and in food packaging. From a disposalperspective, an ionic liquid that is water-soluble is more desirablethan one of the classes of water-insoluble, hydrophobic ionic liquids.

[0060] It has been shown that the addition of non-ionic liquidco-solvents, or solutes can have a profound effect on the physicalproperties of ionic liquids. Melting points and viscosity can besignificantly reduced by the presence of even small concentrations (lessthan 5 percent) of an additive, for example water, ethanol,dimethylsufoxide, or 1-methylimidazole.

[0061] Each of the patents, applications and articles cited herein isincorporated by reference. The use of the article “a” or “an” isintended to include one or more.

[0062] From the foregoing, it will be observed that numerousmodifications and variations can be effected without departing from thetrue spirit and scope of the present invention. It is to be understoodthat no limitation with respect to the specific examples presented isintended or should be inferred. The disclosure is intended to cover bythe appended claims modifications as fall within the scope of theclaims.

What is claimed is:
 1. A temperature sensor using a liquid, the sensorcomprising: a thermometer, having an elongated vessel and a reservoirfor liquid; the thermometer further comprising a bore, within theelongated vessel, the bore being in liquid communication with thereservoir; at least one graduation, associated with the elongatedvessel; wherein the liquid is a thermometric ionic liquid which rises orfalls, within the bore, depending on the temperature ambient to thethermometer.
 2. The temperature sensor of claim 1, wherein thethermometer measures temperatures in a range of about −100° to about+400° Centigrade.
 3. The temperature sensor of claim 1, including aplurality of graduations.
 4. The temperature sensor of claim 3, whereinthe plurality of graduations includes a sufficient number to express arange of temperatures equivalent to about −100° to about +400°Centigrade.
 5. The temperature sensor of claim 1, wherein a contrastmedium is added to the liquid such that the level of the liquid in thebore may be more easily seen.
 6. The temperature sensor of claim 1,wherein a colored dye is added to the liquid such that the level of theliquid in the bore may be more easily seen.
 7. The temperature sensor ofclaim 1, wherein the space within the bore is a vacuum.
 8. Thetemperature sensor of claim 1, wherein the volume of liquid in the boreis dependent on temperature.
 9. The temperature sensor of claim 1,wherein the elongated vessel is created from a transparent material. 10.A temperature sensor using a liquid, the sensor comprising: athermometer, having an elongated vessel and a reservoir for liquid; thethermometer further comprising a bore, within the elongated vessel, thebore being in liquid communication with the reservoir; a plurality ofgraduations associated with the elongated vessel, said graduationsexpressing a range of temperatures equivalent to about −100° to about+400° Centigrade; wherein the liquid is a thermometric ionic liquid,which rises or falls within the bore depending on the temperatureambient to the thermometer and including a contrast medium such that thelevel of the liquid in the bore can be more easily seen; and wherein thethermometer measures temperatures in a range of about −100° to about+400° Centigrade.
 11. The temperature sensor of claim 10, wherein acolored dye is added to the liquid such that the level of the liquid inthe bore may be more easily seen.
 12. The temperature sensor of claim10, wherein the space within the bore is a vacuum.
 13. The temperaturesensor of claim 10, wherein the volume of liquid in the bore isdependent on temperature.
 14. The temperature sensor of claim 10,wherein the elongated vessel is created from a transparent material. 15.The temperature sensor of claim 1 wherein the ionic liquid is comprisedof an organic cation and an organic anion or mixtures thereof.
 16. Thetemperature sensor of claim 1 wherein the ionic liquid is comprised ofan organic cation and an inorganic anion or mixtures thereof.
 17. Thetemperature sensor of claim 15 wherein the organic cation is selectedfrom the group consisting of substituted pyridinium, pyridazinium,pyrimidinium, pyrazinium, pyrazolium, imidazolium, oxazolium,triazolium, thiazolium, pyrrolidinium, piperazinium, quinolinium,isoquinolinium, ammonium, and phosphonium derivatives and mixturesthereof.
 18. The temperature sensor of claim 15 wherein the organiccation corresponds in structure to a formula selected from the groupconsisting of

wherein R¹ and R² are independently hydrido, a C₁-C₆ alkyl group or aC₁-C₆ alkoxyalkyl group, and R³, R⁴, R⁵, R⁶, R⁷, R⁸ and R⁹ (R³-R⁹), whenpresent, are independently a hydrido, a C₁-C₆ alkyl, a C₁-C₆ alkoxyalkylgroup or a C₁-C₆ alkoxy group, and the anion is selected from the groupconsisting of a halogen, pseudohalogen, a C₁-C₆ carboxylate,tetrafluoroborate, hexafluorophosphate, a polyfluoro C₂-C₆ carboxylate,bis(trifluoromethanesulfonyl)imide, and trifluoromethanesulfonate. 19.The temperature sensor of claim 15 wherein the organic cation is asingle, five-membered aromatic ring that is free of fusion to other ringstructures.
 20. The temperature sensor of claim 19 wherein the ionicliquid comprises an organic cation that corresponds in structure to aformula selected from the group consisting of

wherein R¹ and R² are independently hydrido, a C₁-C₆ alkyl group or aC₁-C₆ alkoxyalkyl group, and R³, R⁴, R⁵ (R³-R⁵) are independently ahydrido, a C₁-C₆ alkyl group, a C₁-C₆ alkoxyalkyl group or a C₁-C₆alkoxy group.
 21. The temperature sensor of claim 20 wherein the ionicliquid comprises a 1,3-di-C₁-C₆-alkyl imidazolium ion.
 22. Thetemperature sensor of claim 21 wherein the ionic liquid comprises anorganic cation with C₁-C₆ alkyl groups selected from the groupconsisting of methyl, ethyl, propyl, iso-propyl, butyl, sec-butyl,iso-butyl, pentyl, iso-pentyl, hexyl, 2-ethylbutyl, and 2-methylpentyl.23. The temperature sensor of claim 15 wherein the organic cation is a1-C₁-C₆-alkyl-3-methylimidazolium or a C₁-C₆alkoxyalkyl-3-methylimidazolium cation.
 24. The temperature sensor ofclaim 20 wherein the ionic liquid comprises an organic cation of theformula

wherein R¹ and R² are independently a C₁-C₆-alkyl group or aC₁-C₆-alkoxyalkyl group, and R³, R⁴, R⁵ (R³-R⁵) are independently ahydrido, a C₁-C₆ alkyl group, a C₁-C₆ alkoxyalkyl group or a C₁-C₆alkoxy group.
 25. The temperature sensor of claim 21 wherein the ionicliquid comprises an organic cation whose structure corresponds toformula B

wherein R¹ is a C₁-C₆-alkyl group.
 26. The temperature sensor of claim15 wherein the anion is selected from the group consisting oftetrafluoroborate, hexafluorophosphate, polyfluorocarboxylate,trifluoroacetate, pentafluoropropionate,bis(trifluoromethanesulfonyl)imide and trifluoromethane sulfonate. 27.The temperature sensor of claim 1 wherein the holder is partiallytransparent or translucent.
 28. The temperature sensor of claim 27wherein the holder is glass.
 29. The temperature sensor of claim 5wherein the colored dye is itself an ionic liquid, an imidazoliumtetrachlorometallate salt or mixtures thereof.
 30. A temperature sensorcomprising a holder containing 1-butyl-3-methylimidazoliumbis(trifluoromethanesulfonyl)imide.
 31. A temperature sensor comprisinga holder containing 1-ethyl-3-methylimidazolium tetrafluoroborate.